U.S. Pat. No. 3,383,092 issued to J. M. Cazier on May 14, 1968 shows an energy extraction system for the exhaust flow from a multi-cylinder engine. One of the systems shown in this patent includes an axial flow turbine (FIGS. 7 and 8) for converting exhaust pulses from the individual cylinders into turbine rotation. The cylinders are arranged to direct the exhaust pulses into two separate stacks or manifolds 17 and 18 leading to separate inlets for a single common turbine rotor.
U.S. Pat. No. 3,961,484 issued to me on June 8, 1976 discloses a "stack-value area" sizing system which minimizes throttling losses across the exhaust valves for the cylinders. Each exhaust stack is sized to have less flow area than the associated valve, thereby avoiding the expansion turbulence that otherwise occurs in conventional arrangements wherein the stack has a greater flow area than the associated valve.
The present invention is directed to a system that is generally similar to that shown in U.S. Pat. No. 3,383,092, except that a second radial flow turbine is arranged downstream from the axial flow turbine. The axial flow turbine is equipped with an inlet volute designed to convey the individual pressure pulses to the turbine rotor at substantially pulse initiation velocity, i.e., there is a minimum slowdown or velocity deceleration between the individual cylinders and the turbine rotor. The rotor of the axial flow turbine is preferably designed for dual use as a turbine and a pump; during pulse-flow periods the rotor acts as a turbine, and during the no-pulse periods the rotor acts as a pump to produce a suction effect in the turbine inlet.
Flow output of the axial flow turbine is directed through a diffuser that converts velocity pressure to static pressure with minimum turbulence losses. The resultant essentially steady state flow is applied to the aforementioned radial flow turbine. The individual turbines are preferably connected to different power-absorbing devices. For example, the axial flow turbine may be used to drive a turbocharger for the engine supply air, while the radial flow turbine may be geared to the engine output shaft to contribute added engine output power.
The present invention may be used in an engine system that includes structural relationships embodying my earlier U.S. Pat. No. 3,961,484.